Air flow meter

ABSTRACT

Support member  7  where flow amount detection element  9  including a heating resistor and electronic circuit parts  8  for obtaining the air flow amount according to the flow amount signal detected by flow amount detection element  9  are mounted is cooled from both the direction of the main flow of main passage  2  and the direction of an anti-main flow (the opposite direction to the direction of the main flow).

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a thermal type air flow meter which uses the heating resistor to measure the fluid flow rate such as an intake air flow in an internal combustion engine, for example, for an automobile.

[0002] As a flow amount measuring device by which the intake air flow of the internal combustion engine such as automobiles is measured, the device which measures flow amount according to the heat radiation amount from a heating resistor which corresponds to flow amount, obtained by heating the heating resistor is known in general. Further, a thermal type air flow meter which measures flow amount by heating a heating resistor, and detecting the change in temperature of a temperature sensitive resistor arranged in the neighborhood of the heating resistor is known.

[0003] By the way, the electronic circuit parts (electronic components) which drive the flow amount detection element including a heating resistor and the flow amount measuring device are mounted on the supporting substrate (support member such as circuit boards) made of electrical insulating material with large thermal conductivity such as ceramic etc.

[0004] The miniaturization of the flow amount measuring device advances with the object such as the cost decrease and the decrease of the number of parts of the flow amount measuring device, and the flow amount detection element comes to be mounted on the position near the electronic circuit parts in recent years. Therefore, it is easy to conduct to the flow amount detection element in the heat by the self-heating of the electronic circuit parts, the heat becomes a factor to increase the measurement error.

[0005] In order to solve this problem, the technology is known in which heat is radiated outside by putting the metallic plate on the circuit board where the electronic circuit parts are mounted, and exposing a cooling wheel of the metallic plate in the fluid channel (for instance, the Japanese Patent Application Laid-Open No. 5-231899). Further, the technology is also known in which the flow amount detection element is mounted on the circuit board where the electronic circuit parts are mounted, the window or the notch part is formed between the two, and the part where the electronic circuit of the circuit board was mounted and the part where the flow amount detection element was mounted thermal are thermally shielded (for instance, the Japanese Patent Application Laid-Open No. 9-145440).

[0006] In the prior art, the cooling is carried out just from one direction where air flows. It cannot suppress the heat influence on the flow amount detection element because of the low cooling efficiency. Especially, there is a problem that the accuracy of measurement is deteriorated in the miniaturized thermal type air flow meter.

[0007] Further, the influence of the heat of the main passage besides the heat influence by the self-heating of the electronic circuit parts is received in this kind of thermal type air flow meter. Therefore, the heat influence cannot be suppressed enough, and measures of the more efficient cooling and the heat separation are requested.

[0008] The influence of the heat of the main passage is that the heat of the main passage is conducted to the flow amount detection element when the temperature of the fluid which flows in the inside is low though the temperature of the main passage is high, and the measurement error increases. For instance, there is the case that although the temperature of the outside air is low and thus the temperature of the intake air in the intake pipe, the intake pipe itself is warm because it receives the heat of the engine in the intake pipe for an automobile engine Because the heat of the main passage (In this case, an intake pipe) is conducted to the flow amount detection element through the housing case and the support body of the flow amount detection element in such a state, the conducted temperature becomes the factor of the measurement error.

[0009] Further, the metallic plate might corrode according to the environment when the metallic plate is exposed in the fluid channel as a cooling wheel in the above-mentioned prior art. Further, there is a problem on practical use that mechanical strength decreases when the window or the notch part is formed in the circuit board.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide a thermal type air flow meter which can measure accurately the flow amount without being influenced by the self-heating of the electronic circuit parts and the heat of the main passage by cooling the route of thermal conduction to the flow amount detection element efficiently.

[0011] In the characteristic of the present invention, support member where flow amount detection element including a heating resistor and electronic circuit parts are mounted is cooled from both the direction of the main flow of main passage and the direction of an anti-main flow (the opposite direction to the direction of the main flow).

[0012] Concretely, the present invention includes a housing for accomodating said electronic circuit parts mounted on the said support member, and an auxiliary passage body which forms a flow path for cooling said support member by said fluid which flows in the direction of the main flow of said main passage, and an auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said main passage, the fluid detection element mounted on said support member being provided in the opposite-direction passage portion. The auxiliary passage having a curved portion, which is usually called the curved auxiliary passage is formed in the auxiliary passage body of the present invention.

[0013] Because the support member where flow amount detection element including a heating resistor and electronic circuit parts are mounted is cooled from both the direction of the main flow of main passage and the direction of an anti-main flow (the opposite direction to the direction of the main flow) in the present invention, it is possible to measure accurately the flow amount without being influenced by the self-heating of the electronic circuit parts and the heat of the main passage by cooling the route of thermal conduction to the flow amount detection element efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a sectional view of thermal type air flow meter according to one embodiment of the present invention.

[0015]FIG. 2 is a plan view seen from the direction of the main flow of the main passage of FIG. 1.

[0016]FIG. 3 is a schematic view showing one example of the support member according to the present invention.

[0017]FIG. 4 is a partially broken and enlarged view showing the substantial part of FIG. 1.

[0018]FIG. 5 is a sectional view of thermal type air flow meter according to another embodiment of the present invention.

[0019]FIG. 6 is a plan view showing the substantial part of another embodiment of the present invention.

[0020]FIG. 7 is a partially broken and enlarged view showing the substantial part of FIG. 6.

[0021]FIG. 8 is a sectional view showing the substantial part of a further embodiment of the present invention.

[0022]FIG. 9 is a side view of FIG. 8 seen from the direction of the main flow of the main passage.

[0023]FIG. 10 is a sectional view taken along the line A-A′ of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereafter, embodiments of the present invention will be explained with reference to the drawings.

[0025] One embodiment of the present invention is shown in FIG. 1 and FIG. 2. FIG. 1 is a sectional view of thermal type air flow meter. FIG. 2 is a plan seen from the direction of the main flow of the main passage.

[0026] In FIG. 1 and FIG. 2, flow amount detection element 9 including a heating resistor and electronic circuit parts 8 which composes thermal type air flow meter 1 are mounted on different positions in the long direction of supporting substrate 7 (support member). The enlarged view of these components is shown in FIG. 3. Supporting substrate 7 is formed with a rectangular ceramic material etc. Electronic circuit part 8 is mounted on one side 7A of the side of main passage body 2 in the long direction, and flow amount detection element 9 is mounted on the other side 7B. Main passage body 2 is an intake pipe etc. of the internal combustion engine, and it is occasionally called a main passage thereafter.

[0027] Electronic circuit parts 8 mounted on supporting substrate 7 are accomodated in accomodation room 4R of housing case 4. Further, flow amount detection element 9 including the heating resistor mounted on supporting substrate 7 is arranged in spiral auxiliary passage 5 formed in auxiliary passage body 3. The swirl of auxiliary passage 5 is swirled counterclockwise. The fluid (air) which flows in main passage body 2 flows in from entrance opening 10, and flows out from exit opening 11.

[0028] The other side 7B of supporting substrate 7 where flow amount detection element 9 is mounted is provided in the auxiliary passage part (opposite direction passage part) where the airflow flows in the direction of an anti-main flow which is the direction opposite to the direction of the main flow of the fluid which flows in main passage body 2.

[0029] Housing case 4 and auxiliary passage body 3 are molded integrally, and flow path 6 is terebrated between housing case 4 and auxiliary passage body 3. Flow path 6 is a square hole terebrated in rectangular auxiliary passage body 3 almost in parallel in the direction of the main flow (forward direction) of the fluid which flows in main passage body 2 as shown in FIG. 4. The part of flow path 6 of supporting substrate 7 comes to be exposed to the fluid which flows in main passage body 2.

[0030] Electronic circuit parts 8 are connected to connector 13 by a signal line. Connector 13 penetrates through flange 14. Flange 14 is formed almost like the rectangle, and the screw holes are terebrated in two corner parts.

[0031] Thermal type air flow meter 1 is installed in the hole provided in main passage body 2 as shown in FIG. 1, and fixed in the screw hole of flange 14 by using screw 15 to mount on main passage body 2.

[0032] In this configuration, the fluid (air) flows in flow path 6 in the direction of the main flow of main passage body 2, and flows into spiral auxiliary passage 5 from the entrance opening 10. Flow path arrangement part 7C of supporting substrate 7 shown in FIG. 4 is cooled by the airflow flowed in the direction of the main flow.

[0033] On the other hand, the air flowed into spiral auxiliary passage 5 from entrance opening 10 is guided like a swirl and flowed out from exit opening 11. The velocity of the airflow which flows in auxiliary passage 5 is detected by flow amount detection element 9, and is input to electronic circuit parts 8 to measure the air flow rate. Because it is known well to measure the air flow rate by electronic circuit parts 8, the detailed description is omitted here.

[0034] Now, although the air which flows in spiral auxiliary passage 5 cools the other side 7B of supporting substrate 7, the direction of the airflow to cool the other side 7B becomes the opposite direction (the direction of an anti-main flow) to the flow direction of flow path 6 or the main flow direction of main passage body 2. Therefore, the other side 7B of supporting substrate 7 is cooled by two airflows of which flow directions are different about by 180° from each other.

[0035] Similarly, upper wall 3A of auxiliary passage body 3 is also cooled by two airflows, the airflow which flows through flow path 6 and the airflow which flows through auxiliary passage 5, of which flow directions are different about 180° from each other.

[0036] Thus, the other side 7B of supporting substrate 7 where flow amount detection element 9 is cooled by two airflows, the airflow which flows through flow path 6 and the airflow which flows through auxiliary passage 5, of which flow directions are different about 180° from each other. In other words, supporting substrate 7 is cooled from both sides of the main passage upstream side and the main passage downstream side. Further, upper wall 3A of auxiliary passage body 3 is also cooled from both sides of the main passage upstream side and the main passage downstream side.

[0037] Because the flow of air which cools supporting substrate 7 in auxiliary passage 5 takes the direction opposed to the direction of the main flow of main passage 2, and flows toward the main passage upstream side from the main passage downstream side, the main passage downstream side of upper wall 3A of auxiliary passage body 3 and supporting substrate 7 are cooled efficiently.

[0038] On the other hand, because the airflow in flow path 6 flows from the same main passage upstream side as the direction of the main flow of main passage 2, the main passage downstream side of upper wall 3A of auxiliary passage body 3 and supporting substrate 7 are cooled efficiently.

[0039] Since upper wall 3A of auxiliary passage body 3 and supporting substrate 7 are cooled from both sides of the main passage upstream side and the main passage downstream side by two airflows of which flow directions are different about 180° from each other, they are cooled very efficiently. Since upper wall 3A of auxiliary passage body 3 and supporting substrate 7 are cooled very efficiently, the heat of main passage body 2 and the heat by the self-heating of electronic circuit parts 8 come not to conduct easily to flow amount detection elements 9. After all, the measurement error of the flow amount can be reduced, and the flow amount can be measured with a high degree of accuracy.

[0040] Further, if not metal but ceramic material is used as the supporting substrate, it is possible to prevent from corroding even if the supporting substrate is exposed in the flow of the main passage. However, because the thermal conductivity of the ceramic material is lower than metal, the efficiency of heat dissipation worsens while the heat conducted to the flow amount detection element lowers.

[0041] Further, apparent thermal conduction in the supporting substrate improves by forming the internal conductor to the all aspects by using the accumulating substrate for the supporting substrate, and the efficiency of heat radiation efficiency improves. In this case, measures such as providing the area where the wiring density of the internal conductor is small around the flow amount detection element are necessary because it should be made easily not to conduct to the flow amount detection element in heat.

[0042] Another embodiment of the present invention is shown in FIG. 5. FIG. 5 is a sectional view of thermal type air flow meter.

[0043] The point where the embodiment shown in FIG. 5 is different from the embodiment of FIG. 1 is that auxiliary passage 5 formed to auxiliary passage body 3 is in

-shape.

[0044] Also in the embodiment of FIG. 5, the air flowed into

-shaped auxiliary passage 5 from entrance opening 10 is guided like

-shape and flowed out from exit opening 11.

[0045] Although the air which flows in

-shaped auxiliary passage 5 cools the other side 7B of supporting substrate 7, the direction of the airflow to cool the other side 7B becomes the opposite direction (the direction of an anti-main flow) to the flow direction of flow path 6 or the main flow direction of main passage body 2. Therefore, the other side 7B of supporting substrate 7 is cooled by two airflows, the airflow which flows through flow path 6 and the airflow which flows through auxiliary passage 5, of which flow directions are different about by 180° from each other.

[0046] Similarly, upper wall 3A of auxiliary passage body 3 is also cooled by two airflows, the airflow which flows through flow path 6 and the airflow which flows through auxiliary passage 5, of which flow directions are different about 180° from each other.

[0047] In the embodiment of FIG. 5 as well as the embodiment shown in FIG. 1 and FIG. 2, supporting substrate 7 is cooled from both sides of the main passage upstream side and the main passage downstream side. Further, upper wall 3A of auxiliary passage body 3 is also cooled from both sides of the main passage upstream side and the main passage downstream side. Since upper wall 3A of auxiliary passage body 3 and supporting substrate 7 are cooled very efficiently, the heat of main passage body 2 and the heat by the self-heating of electronic circuit parts 8 come not to conduct easily to flow amount detection elements 9. After all, the measurement error of the flow amount can be reduced, and the flow amount can be measured with a high degree of accuracy.

[0048] The substantial part of a further embodiment of the present invention is shown in FIG. 6 and FIG. 7. FIG. 6 is a plan view seen from the direction of the main flow of the main passage. FIG. 7 is a partially broken and enlarged view of the auxiliary passage.

[0049]FIG. 6 and FIG. 7 show configuration in which ditch 17 is formed in auxiliary passage body 3 instead of flow path 6 of FIG. 4 and by which supporting substrate 7 is cooled. Thus, supporting substrate 7 can be cooled by the air in the direction of the main flow of main passage 2 even in this configuration.

[0050] Further, because the surface of the other side of ditch 17 can use as accomodation room 4R of housing case 4, and mount electronic circuit parts 8 connected electrically to flow amount detection element 9, it is possible to make smaller.

[0051] The substantial part of a further embodiment of the present invention is shown in FIG. 8, FIG. 9, and FIG. 10. FIG. 8 is a sectional view of the substantial part of the thermal type air flow meter. FIG. 9 is a side view seen from the direction of the main flow of the main passage in FIG. 8. And, FIG. 10 is a sectional view taken along the line A-A′ of FIG. 8.

[0052] In the embodiment shown in FIG. 8 to FIG. 10, auxiliary passage 5 is formed by providing a curved portion in the same surface, and exit opening 11 is formed under auxiliary passage body 3. Further, Flow path 6 is provided at the position adjacent to auxiliary passage 5 of auxiliary passage body 3, and supporting substrate 7 is arranged between auxiliary passage 5 and flow path 6.

[0053] In the embodiment of FIG. 8 to FIG. 10 as well as the embodiment shown in FIG. 1 and FIG. 2, supporting substrate 7 is cooled from both sides of the main passage upstream side and the main passage downstream side. Since supporting substrate 7 is cooled efficiently, the heat of main passage body 2 and the heat by the self-heating of electronic circuit parts 8 come not to conduct easily to flow amount detection elements 9. After all, the measurement error of the flow amount can be reduced, and the flow amount can be measured with a high degree of accuracy.

[0054] The fluid flow rate can be measured as mentioned above. Because the support member where flow amount detection element including a heating resistor and electronic circuit parts are mounted is cooled from both the direction of the main flow of main passage and the direction of an anti-main flow (the opposite direction to the direction of the main flow) in the present invention, it is possible to measure accurately the flow amount without being influenced by the self-heating of the electronic circuit parts and the heat of the main passage by cooling the route of thermal conduction to the flow amount detection element efficiently.

[0055] Although the angle of the direction of an anti-main flow (opposite direction to the direction of the main flow) with respect to the direction of the main flow of the main passage is set to about 180° in the above-mentioned embodiment, another angle can be used.

[0056] It is clearly appreciated that the housing and the auxiliary passage body can be molded separately without molding integrally. 

What is claimed is:
 1. A thermal type air flow meter having a flow amount detection element including a heating resistor and electronic circuit parts mounted on the same support member, for measuring the flow amount of the fluid which flows in the main passage, comprising: a housing for accomodating said electronic circuit parts mounted on the said support member; an auxiliary passage body which forms a flow path for cooling said support member by said fluid which flows in the direction of the main flow of said main passage, and an auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said main passage, the fluid detection element mounted on said support member being provided in the opposite-direction passage portion.
 2. A thermal type air flow meter having a flow amount detection element including a heating resistor and electronic circuit parts mounted on the same support member, for measuring the flow amount of the fluid which flows in the main passage, a housing for accomodating said electronic circuit parts mounted on the said support member, and an auxiliary passage body which forms the auxiliary passage with a curved portion, wherein said housing and said auxiliary passage body are molded integrally, and wherein an auxiliary passage body forms a flow path for cooling said support member by said fluid which flows in the direction of the main flow of said main passage, and an auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said main passage, the fluid detection element mounted on said support member being provided in the opposite-direction passage portion.
 3. A thermal type air flow meter having a flow amount detection element including a heating resistor and electronic circuit parts mounted on the same support member, for measuring the flow amount of the fluid which flows in the main passage, comprising: a housing for accomodating said electronic circuit parts mounted on the said support member; an auxiliary passage body provided under said housing, which forms a curved auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said main passage, the fluid detection element mounted on said support member being provided in the opposite-direction passage portion; and a flow path provided almost in parallel with the direction of the main flow of said main passage, and between said housing and said auxiliary passage body, for cooling said support member by said fluid which flows in the direction of the main flow of said main passage.
 4. A thermal type air flow meter having a flow amount detection element including a heating resistor and electronic circuit parts mounted on different positions of a long direction of a rectangular support member, for measuring the flow amount of the fluid which flows in the main passage, comprising: a housing for accomodating one side of said rectangular support member on which said electronic circuit parts mounted; an auxiliary passage body which forms a curved auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said main passage, the fluid detection element mounted on said support member being provided in the opposite-direction passage portion; and a flow path provided almost in parallel with the direction of the main flow of said main passage, for cooling the other side of said support member by said fluid which flows in the direction of the main flow of said main passage.
 5. A thermal type air flow meter having a flow amount detection element including a heating resistor and electronic circuit parts mounted on a rectangular support member, for measuring the flow amount of the fluid which flows in the main passage, comprising: a housing for accomodating said electronic circuit parts mounted on one end of said main passage side of said rectangular support member; an auxiliary passage body which forms a spiral auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said main passage, the fluid detection element mounted on the other side of said support member being provided in the spiral auxiliary passage; and a flow path provided almost in parallel with the direction of the main flow of said main passage, for cooling the other side of said support member by said fluid which flows in the direction of the main flow of said main passage.
 6. A thermal type air flow meter having a flow amount detection element including a heating resistor and electronic circuit parts mounted on a rectangular support member, for measuring the flow amount of the fluid which flows in an intake pipe, the air flow meter being provided in the intake pipe, comprising: a housing for accomodating said electronic circuit parts mounted on one end of the intake pipe side of said rectangular support member; an auxiliary passage body which forms a spiral auxiliary passage with an opposite-direction passage portion where said fluid flows in the opposite direction to the direction of the main flow of said intake pipe, the fluid detection element mounted on the other side of said support member being provided in the spiral auxiliary passage; and a flow path provided almost in parallel with the direction of the main flow of said intake pipe, for cooling the other side of said support member by making said air flow. 